A number of neurosurgical procedures, including epilepsy resections, tumor resections and chronic neuroprosthetic implantations, require functional mapping of the conduction within central nervous system. A site in the central nervous system can be stimulated and the subsequent activation from the stimulation can be mapped to understand the conduction in the brain. Generally, such functional mapping requires multiple sites within the central nervous system to be stimulated via electrical stimulation and/or magnetic stimulation.
An electrical stimulation current can be applied to the exposed central nervous system tissue via at least one of the metal contact. The current spreads between the contacts and activates at least part of the exposed central nervous system tissue. A primary limitation of the electrical stimulation probe is due to the contacts being located on the surface of the exposed central nervous system tissue. Accordingly, a predominate amount of current flows between the contacts, and a smaller amount of current flows into the exposed central nervous system tissue. One alternative that can increase the amount of current that flows into the tissue is increasing the amplitude of the current. However, increasing the amplitude of the current reduces the spatial resolution if the electrical stimulation by activating untargeted neurons. Another alternative that can increase the amount of current that flows into the tissue is inserting the probe into the tissue (referred to as penetration mapping). While inserting the probe into the tissue would increase spatial resolution and decrease the stimulation amplitude needed to activate the tissue, penetration mapping techniques are not typically used at least because inserting the probe into the tissue may lead to surgical complications and damage of tissue that is otherwise normal.
Traditional magnetic stimulation techniques use magnetic induction to activate at least part of the central nervous system. While these magnetic stimulation techniques do not require the central nervous system to be exposed, they suffer from a lack of specificity so that the activation cannot be mapped accurately. Additionally, traditional magnetic stimulation techniques employ a large inductor coil (e.g., many centimeters in size) that requires a large power source, adding additional instrumentation to the surgical area and generates a large current that can induce heating in metal objects, such as surgical instruments.